The present invention relates to a fringe field switching liquid crystal display(xe2x80x9cLCDxe2x80x9d), and more particularly to a fringe field switching LCD reducing vertical components of a fringe field that is generated between a counter electrode and a pixel electrode.
Generally, the fringe field switching liquid crystal display(xe2x80x9cFFS-LCDxe2x80x9d) is proposed to substitute a general in-plane switching liquid crystal display(xe2x80x9cIPS-LCDxe2x80x9d) having low aperture ratio and transmittance, a corresponding patent application has been filed in the Rep. of Korea in application number of 98-9243.
The foregoing FFS-LCD includes upper and lower substrates being separated with a selected cell gap, a liquid crystal layer, and counter and pixel electrodes formed at an inner surface of the lower substrate. The counter and the pixel electrodes are made of transparent conductor, a distance between the counter electrode and the pixel electrode is smaller than the cell gap. As a result, fringe fields are formed between electrodes and on the electrodes.
FIG. 1 is a plane view of a lower substrate structure of the FFS-LCD.
Referring to FIG. 1, a gate bus line 3 and a data bus line 7 are disposed on a lower substrate 1 in a cross or a matrix type, thereby defining a sub pixel Pix. A thin film transistor TFT is disposed adjacent to an intersection of the gate bus line 3 and the data bus line 7. A counter electrode 2 is made of transparent conductor and is formed at each sub pixel Pix. Here, the counter electrode 2 is in shape of a rectangular plate or a comb. A common signal line 30 for continuously providing common signals to the counter electrode 2, is disposed in contact with the counter electrode 2. Herein, the common signal line 30 is made of a metal layer having excellent signal transmittance property, generally a metal layer for gate bus line. In addition, the common signal line 30 includes a first part 30a being parallel to the gate bus line 3 and being in contact with a selected portion of the counter electrode 2, and a second part 30b being extended from the first part 30a parallel to the data bus line 7 and being disposed between the counter electrode 2 and the data bus line 7. A pixel electrode 9 is formed at the sub pixel Pix so that the pixel electrode 9 overlaps with the counter electrode 2. At this time, the pixel electrode 9 is electrically insulated from the counter electrode 2. The pixel electrode 9 is formed in shape of a comb, and includes a tooth part 9a having a plurality of teeth which are disposed parallel to the data bus line 7 and arranged with a uniform distance from each other, and a bar 9b contacting one end of the tooth part 9a and being in contact with a selected portion of the thin film transistor TFT. Meanwhile, although not shown in drawings, an upper substrate opposing the lower substrate 1 is opposed with a greater distance than that of the pixel electrode 9 and the counter electrode 5.
Operation of the foregoing FFS-LCD is as follows. When an electric field is formed between the counter electrode 5 and the pixel electrode 9, the distance between the counter electrode 5 and the pixel electrode 9, i.e. the thickness of gate insulating layer is greater than that of the upper and the lower substrates, thereby generating a fringe field between and on the electrodes. The fringe field influences over the entire counter electrode 5 and the pixel electrode 9, thereby driving all liquid crystal molecules on the electrodes. Accordingly, high aperture ratio and high transmittance are realized.
However, the conventional FFS-LCD has following problems.
First, since the distance between the tooth part 9a of the pixel electrode 9 and the counter electrode 5 is smaller than the cell gap, i.e. the distance between upper and lower substrates, vertical components exist in the fringe field.
These vertical components of the fringe field are only generated on upper region of the electrodes, and long axes of the liquid crystal molecules which should be parallel to the substrates are disposed almost vertical to the substrates. Therefore, mis-alingment of the liquid crystal molecules results and there is found some defects in the picture quality.
Moreover, the vertical components FA of the fringe field are shown in the different types, as shown in FIGS. 2 and 3, with respect to the (+) frame of LCD and (xe2x88x92) frame of LCD. Accordingly, arrangements of liquid crystal molecules 10a in the (+) frame in the (xe2x88x92) frame are different from each other, a difference in the brightness occurs. Due to the difference in the brightness, a DC bias is applied to the liquid crystal layer thereby degrading the liquid crystal molecules. As a result, the defect in the picture quality occurs.
Accordingly, the object of the present invention is to provide an FFS-LCD capable of minimizing the vertical components of the fringe field and improving picture quality.
To accomplish the foregoing object, one embodiment of the present invention provides an FFS-LCD including: a lower substrate; a gate bus line extended on the lower substrate in a selected direction; a data bus line disposed to cross the gate bus line, thereby defining a sub pixel; a thin film transistor disposed at an intersection of the gate bus line and the data bus line; a counter electrode formed at each sub pixel and formed in shape of a rectangular plate, the counter electrode to which a common signal is continuously transmitted; and a pixel electrode electrically connected to the thin film transistor and comprising a plurality of teeth which are overlapped with the counter electrode so as to form a fringe field with the counter electrode, wherein the counter comprises a plurality of slits, and the slits are disposed between the teeth of the pixel electrode, and the counter electrode and the pixel electrode are made of a transparent conductor.
Further, another embodiment of the present invention provides an FFS-LCD including: a lower substrate; a gate bus line extended on the lower substrate in a selected direction; a data bus line disposed to cross the gate bus line, thereby defining a sub pixel; a thin film transistor disposed at an intersection of the gate bus line and the data bus line; a counter electrode formed at each sub pixel and formed in shape of a rectangular plate, the counter electrode to which a common signal is continuously transmitted; and a pixel electrode electrically connected to the thin film transistor and comprising a plurality of teeth which are overlapped with the counter electrode so as to form a fringe field and the teeth are parallel with the data bus line, wherein the counter comprises a plurality of slits, and the slits are disposed between the teeth of the pixel electrode, and the counter electrode and the pixel electrode are made of a transparent conductor.